Loans Receivable and Related Allowance for Loan Losses - Activity in Allowance for Loan Losses by Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Allowance for loan losses:
Beginning Balance	$ 5,688	$ 5,352	$ 5,545	$ 5,205	$ 5,205
Charge-offs	(128)	(47)	(174)	(88)
Recoveries	6	5	33	12
Provision	201	121	363	302
Ending Balance	5,767	5,431	5,767	5,431	5,545
Ending ALL balance attributable to loans:
Individually evaluated for impairment	8		8		120
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	5,759		5,759		5,425
Total loans:
Individually evaluated for impairment	2,017		2,017		1,833
Acquired loans collectively evaluated for impairment			51,697		58,936
Originated loans collectively evaluated for impairment	497,819		497,819		460,211
Total	551,533		551,533		520,980
Residential Mortgages
Allowance for loan losses:
Beginning Balance	1,956	1,577	1,846	1,429	1,429
Charge-offs	(10)	(8)	(36)	(40)
Recoveries	0	0	0	0
Provision	48	127	184	307
Ending Balance	1,994	1,696	1,994	1,696	1,846
Ending ALL balance attributable to loans:
Individually evaluated for impairment	8		8		19
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	1,986		1,986		1,827
Total loans:
Individually evaluated for impairment	442		442		135
Acquired loans collectively evaluated for impairment			21,849		25,024
Originated loans collectively evaluated for impairment	192,614		192,614		173,008
Total	214,905		214,905		198,167
Home Equity & Lines of Credit
Allowance for loan losses:
Beginning Balance	648	636	633	586	586
Charge-offs	(10)	(33)	(11)	(33)
Recoveries	1	1	20	1
Provision	0	41	(3)	91
Ending Balance	639	645	639	645	633
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	639		639		633
Total loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			4,324		5,225
Originated loans collectively evaluated for impairment	86,412		86,412		86,134
Total	90,736		90,736		91,359
Commercial Real Estate
Allowance for loan losses:
Beginning Balance	2,449	1,926	2,314	2,185	2,185
Charge-offs	(90)	0	(90)	0
Recoveries	2	3	4	7
Provision	99	189	232	(74)
Ending Balance	2,460	2,118	2,460	2,118	2,314
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		95
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	2,460		2,460		2,219
Total loans:
Individually evaluated for impairment	975		975		1,014
Acquired loans collectively evaluated for impairment			24,486		27,492
Originated loans collectively evaluated for impairment	154,430		154,430		138,488
Total	179,891		179,891		166,994
Commercial Business
Allowance for loan losses:
Beginning Balance	583	1,162	700	960	960
Charge-offs	(10)	0	(10)	0
Recoveries	0	0	0	0
Provision	48	(242)	(69)	(40)
Ending Balance	621	920	621	920	700
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		6
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	621		621		694
Total loans:
Individually evaluated for impairment	600		600		684
Acquired loans collectively evaluated for impairment			1,038		1,182
Originated loans collectively evaluated for impairment	57,159		57,159		55,922
Total	58,797		58,797		57,788
Consumer
Allowance for loan losses:
Beginning Balance	52	51	52	45	45
Charge-offs	(8)	(6)	(27)	(15)
Recoveries	3	1	9	4
Provision	6	6	19	18
Ending Balance	53	$ 52	53	$ 52	52
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	53		53		52
Total loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		13
Originated loans collectively evaluated for impairment	7,204		7,204		6,659
Total	$ 7,204		$ 7,204		$ 6,672